The worst offenders should face tougher sentences at younger ages to deter them from a life of crime, Britain’s top police officer has suggested.

In a speech to the Howard League for Penal Reform, she said some youths were “simply not fearful of how the state will respond to their actions”.

She highlighted the case of one 16-year-old in south London who has committed 42 offences in the space of three years, is involved in gangs, habitually carries a knife and yet has never been jailed.

Ms Dick said one of the consequences of the state’s attempts to deal with young offenders in the community was that they now “don’t see prison as a particularly likely threat”.

Of the teenagers that are jailed, two out of three go on to reoffend within a year of their release.

She said persistent young offenders were having a disproportionate effect on other young people, as the number of ten to 19-year-olds in the capital has increased ten per cent in the last decade.

In some areas the increase has been significantly higher, with Tower Hamlets seeing a 26 per cent increase.

One in three robbery victims is aged 10 to 19, while 26 per cent of rape victims are in this age group along with 16 per cent of sexual offenders, said Ms Dick.

“We also know that many of the perpetrators of violent crime are also victims of violent crime and vice versa,” she said.

The Commissioner also highlighted the disparity between race and violence – of the 24 teenagers murdered in London this year, 21 were black and three were of Asian origin.

She said one of the biggest concerns for young people was seeing others carrying knives and attacking people and “getting away with it”.

Ms Dick argued for a “blend of better engagement by public services” including mental health services, running and funding diversion activities and work in schools to try to prevent young people turning to crime.

She added: “For debate, should we couple that with harsher more effective sentencing used here? It is clear other approaches are no longer working.”

Ms Dick said she had to be “realistic” about rising crime in the capital.

“We need to step in earlier into people’s lives. We need to give more real deterrents and we need to use the opportunity that imprisonment could give to better ensure that children, and we must remember they are children, don’t reoffend,” she said.

Frances Crook, chief executive of the Howard League, said it was “unusual” for a police officer to comment on sentencing.

Following the commissioner’s speech, the Howard League criticised her for focusing on “locking up black boys”.

A spokesman said there was “no evidence” that locking up youths was the solution to rising crime levels among younger age groups.

Andrew Neilson, director of campaigns at the organisation, said: “Cressida Dick was explicitly talking about young black boys. She acknowledged they are often both victims and perpetrators, being criminally exploited by gangs.

“The chief inspector of prisons recently said there was not a single institution in this country holding children that could be considered safe. If the answer to this problem is to lock 13 or 14-year-old black boys up for the remainder of their childhood in institutions sometimes described as ‘warzones’, then that is a counsel of despair.”